Art of tanning



c. C. KROUS E. ART OF TANNING.

APPLICATION IiILED JUNE 20, I919- I Patented Apr. 27, 1920.

' 117214912502: Cizalia Clfmme.

Substitute for application Serial- No. 170,084, .flled May 81, 1917, a renewal of application 170.20,!771

crimes cLEMEN'r Kno sE, or wrnmamsronr, PENNSYLVANIA.

ART or TANNING.

- Specification of Letters Patent.

Patented A 27, 1920.

-fl1ed April 12, 1915. This application filed June 20, 1919. I Serial -No..30 5,460."

To all whom it may concern.-

Be it known that I,'CHARLES- C. KROUSE, I

of Williamsport, Pennsylvania, have in-' v -filed October 26., 1916, whichin'turn was a,

' this latter .being a renewal. o :No.- 20,877,

vented certain new and useful Improvements in the Art of Tannin of which the following is a specification, t is application being a substitute for N0. 170,08 1, filed May 21, 1917, which was a renewal of No. 127,966,

renewal of No. 92,311, filed A ril 19, 1916,

.' filed April 12, 1915.

Mypresent invention relates to improvements in the process of extracting fat from raw hides and skins preparatory totanning, and has among others for its ob'ects to provide a preliminary treatment 0 the raw or pickled skins which not only enables them to be more quickl and eflt'ectu'ally subjectedto the action of t e tanning liquid, but which will produce a superior grade'of leather.

The raw hides and skins of animals, and notably pig and sheep skins, contain a large quantity of animal fat or grease, which is repellent to' tannic acid or tanning liquor,

and in the usual process. of tanning some means is generally employed to neutralize as much of the excess fat as possible, as for instance by immersing for a long time in solution of lime,with additional manipulation by hand when the skins have an excessive quantity of fat; or by drumming the skins in a solution of caustic soda.

By my present invention Ilimit the liming process only to the action of distending the skin fibers, known as plumping which may also be done with acids; or I may do away with the limin process all together. I remove all excess at'or grease from the raw skins, making them more receptive to the tanning liquor which quickly and thoroughly penetrates the interstices or pores of the skins and acts more efficiently upon them to produce leather of'superior quality and strength. 1

My present invention is particularly ad.- vantageous in connection with skins which, after being tanned, are to be colored, or to be provided with a' coating of enamel or like finish for gloves or shoe uppers, such as sheep or goat skins. -Heretofore it has been regarded as necessary to subject the per se no part of the present invention.

.process before such uniformly fine coloring or enamel finish could be'produced, but by particularly defined by the appended claims.

. According to, my invention Iextract the excess grease or animal fat from the raw or pickled and untanned skins, without loss of collogen or otherwise depleting or damaging the skins, by means of a sultable' grease solvent. p

The preferred manner of carryin out my improved process will be describe in connection with the accompanying drawing showing an apparatus capab sentative of any suitable plant, and orming In this drawing: Figure 1 is a longitudinal sectional view, and

In this drawing-the numeral 1 designates a rotary vessel or drum built to withstand inner, and outer pressures and provided preferably with ribs 2 projecting from its inner periphery. The drum is provided with a jacket 3 for heating purposes to which steam or hot water may be supplied from a supply pipe 4 passing throughthe e of carrying out the process, such apparatus bein repre- Fig. 2 is a section on line 2-2 of Fig. 1.

hollow trunnion 5, which communicatesby pipes 6 with the jacket, the outflow from the jacket being by pipe or pipes 7 through the hollow trunnion 8 at the opposite endof the drum and outlet ipe 9. The drum is provided with one or more manholes10 forthe insertion and removal.

of the skins. Through the hollow trunnion passes a pipe 11, which pipe is connected by branch pipes with a vacuum pump, source mospheric pressure as hereinafter described,

those sources for convenience of illustration being omitted.

The drum may be rotated from any source tanned skins "or v hides to an extraction of power, applied to the wheel indicated at 12. In carrying out my improved process by the apparatus as described and according to the preferred manner, I first .cleanse the skins by the usual method of washing or soaking. If received in the hair, bristles, or short wool, I then depilate them by immersion or drumming in a sodium su fid solution which causes the hair to dissolve, after which they are again washed in water to free them from sodium sulfid. Other meth-. ods of depilation maybe used, for instance a paste mixture of lime and sodium sulfid spread upon the hair which dissolves it, followed by a washing. The usual method of liming for depilation may be employed if V desired. I then "load the skins into the drum through the manhole, which is then closed,

and slowly revolve the drum, the vacuum peump being started, and steam or hot water ing turned into the jacket. In the vacuum thus created, the water or moisture is evap. orated from the revolved skins at a tem-- peraturebelow that at which the skins will be dama ed, to wit; at about or below 120 degrees ahrenheit, as a temperature exceeding this will melt 'the collogen in the v vacuum which exists within the drum.

Other methods of dehydrating wet skins may be employed, for instance drumming them in a water absorbing material such as methyl alcohol. By this method after the skins are placed in the drum and the man- I hole is closed, denatured alcohol is pumped into the drum. The drum is slowly revolved for one and one-half hours, after which it is stopped, the water saturated alcohol is drainedinto a still for redistillation, separation and re-use. To evaporate residual alcohol from the skins, vacuum is created within the drum, the drum is slowly revolved, and heat is applied through the jacket. The resultant alcohol vapor is then passed through a cooler or. condenser, and.

the condensed vapor or liquid flows into a storage tank for reuse. It is not essential that all skins be dehydrated for effectual.

fdegreasing. In some cases they may simpl be passed through a rolling machine, whic squeezes out the excess water and loosens or breaks the oil cells, bringing them into condition for effectual degreasing.

Any approved grease solvent may be used such as naphtha, but I prefer trichlorethylene because of its density (specific gravity 1.47), and its noninflammability. After, the

' tank or drum has received the charge of solvent'and is again started in motion, the slow rotation of the drum, aided by the lon itudinal ribs therein, agitate the skins an solvent by tumbling which. facilities penetration. By; employing a solvent of specific" gravity eavier than water, such as that above specified, the resultant pres'sure has a a tendency to press :the remainmg water out of theskins and more freely admit the s'olvent, requiring'the skins to be less dehydrated than when a less dense solvent is used. After the grease or fat is largely dissolved from the skins and the'rotation of the drum is stopped, the grease laden solvent is drained into a still, and fresh solvent is admitted, andthe operation repeated until all of the excess grease is removed from the skins. 30 Rotation is 'then again started and the vacuum recreated if broken while draining, and the jacket is heated to a degree below that at which the skins will be injured. The low heat coupled with thevacuum causes quick evaporization of the .residual solvent at a temperature which precludes injury to the skins, the vapor passing through the vacuum pump to a condenser where it is again turned into a liquid and goes into the storagetank for reuse. The grease laden solvent may be distilled in the usual manner to separate grease and solvent, the solvent being condensed into liquid for reuse, and the grease recovered as a b -product for re.- fining and'marketing. T e skins are unloaded from the drum as free fromgrease as desired, practically dry, and read'yforthe tanning process. I If the extracting drum be lead lined or otherwise protected to prevent the tannic acid from coming into contact with iron, the tannin process could be carried out in-the same um without removing the skins but a .for economic reasons itshould be accom- 105 plished in a separate apparatus. I

-At this stage the hides or skins are, as above stated, as free from grease as desired, practically dry, and in a receptive condition for-tanning liquor, not bein hard or bony 110 like dr hides-or skins 'w ich have been subjecte to-tropical sun drying.

The succeeding tanning operation may be by various methods, depending upon the kinds of hides orskins and the uses to which 115 the leather is to be put; for instance, vegetable tanning (oak or hemltick) or mineral tanning ,(chrome or alum) or a combination of both, with or without a wax filling for water proofing, etc. i 120 I do not claim thatv my process is of Spe: cial benefit in preparing low fat-bearing hides or skins for. tanning; such as cattle and horse=hides, as'the fat content is not sufiicient to seriously interfere with the tan- 125 ning process, but it is especially applicable to bog, sheep and'seal skins. I t is also applicable to goat skin's. v Raw hides and kins may be divided into three general classes, depending on the no ning b the usual processes.

w percentage of fat- 2% to 5%; ap-

proximately cattle and calves, horses and colts, deer, etc.

B. Medium percentage of fat-8% to 15%, approximately goat and kid.

. C. .Highpercentage of fat15% to 25%, p v

y 15% fat yield relatively weak leather;

approximately hogs and pigs, sheep and lambs, seal, etc.

Similarly, the strength or tou hness, and

consequent utility of leather, is argely determined by proportion of natural animal fat contained in the raw hides and skins. Fat or grease repels tanning liquor, and tannic acid will not mix or combine with fat.

With a small proportion of fat in hides or I skins, tanning liquor will penetrate and the tannic acid will combine with' collogen, making tough strong leather; but in proportion to the larger percentage of fat in raw hides or skins the less will tanning -liquor penetrate, and the less efiicientl will tannic acid and collogen combine. herefore generally, the less fat contained in hides or skins, or the more fat' removed before.tanning, the more easily the tanning operation can be performed, but it is not alone a question of ease and economy intanning, but the different and better result of obtaining strong leather from so-called inferior hides or skinsthat would otherwise yield only weak leather. -'An illustration of this is the use of sheep skin leather in-imis tation of kid (goat) gloves. Theonly practical difference between goat and sheep skin 7 leather is that one is relatively strong and the other relatively weak. Sheep skin leather is relatively weak, largely because of imperfect tannage due'to a large proportion of fat. For the same reason the mar: ket price forraw'sheep skins is less than for goat skins. As a general practice, hogs are not now skinned, and the worlds largestpossible supply of animal skins suitable for leather is now practicallylost to the markets and tothe public, at a time when there is a world-wide shortage of hides and skins, simply because hog skins contain a large proportion of fat and will not yield good leather without practical degreasing.

The largest general use for leather is in the manufacture of shoesuppers and soles-'- for which leather made from low fat-bearused, such as goatand kid. In the latter case the skins are almost invariably degreased after'they are tanned, to permit coloring'or enameling, which treatment does not 'increase the strength of the leather. My process of degreasingraw skins preparatory to tanning brings .hog skins iato condition a I be thorou hly tanned, and .makes them available or shoe upper and soleleather,

with a strength and wearing quality equal 1:

toor superior to leather made from cattle hides;

Hides or skins containing from 2% to 5% fat yield strong leather;

Hides or skins containing from 8% to -Hides or skins containing from 15% .to

I 25% fat yield leather with little strength.

tent somewhat higher.

"I claim 1. The herein described method of treating raw hides and skins, containing a high percentage of fat, preparatory to tanning, consisting in adding to the hides and skins" suflicient quantity of grease solvent'to dissolve the grease so that when the solvent is withdrawn it carries enough of'the grease, with it to bring the 'skins into a condition for tanning-to produce strong leather, substantially as described.

2. The herein described method of treat- I ing raw hog skins preparatory to tanning, consisting in adding to such skins a sufiicient quantity of grease solvent to dissolve such a proportion of the grease that when the solvent is withdrawn it carries with it enough grease to leave the skins in condition for tanning to produce strong leather.

3. The-hereindescribed method of treat ing raw hides and skins preparatory to tanning, consisting in extracting the fat from said hides and skins by a volatile solvent and evaporating the residual solvent from the hides and skins while maintaining a temperature below that at which the collogen in the skins will melt, substantially as and for the purpose set forth.

4. The herein described method of treating raw hidesand skins, which originally contained from 8% to 38% of fat, preparatory to. tanning, consisting in extracting the fat from saidhides and skins by. a volatile solvent down to a maximum of 5% remaining in thehides and skins, and evapo-. rating the residual solvent from the hides and skins while maintaining a temperature below that. at which the collogenin the skins will melt. y

5. The herein described method of treating hog skinspreparatory to tanning, conslsting in extracting the fat from said skins, so as to leave therein not more than" 5% by the use of a volatile solvent, and then evaporating the residual solvent at a temperature below that at which the collogen in the skins will melt.

- 6. The herein described method of treating raw hides and skins containing a high 7 percentage of fat which consists in adding to contained between 8% and 38% of fat, preparatory to tanning, which comprlses dehydrating the skins in vacuo, agitating them in a body of volatile solvent, withdrawing vent and repeating the operation IIIItllSllffi:

cient grease is drawn off with the solvent to fit the skins for tanning to produce strong leather.

8. The herein described method of treating raw hides and skins containing va high percentage of fat, preparatory to tanning, consisting in dehydrating the hides and skins, and thereafter adding to them a sufii cient quantity of grease solvent to dissolve the grease so that when the solvent is withdrawn it carries enough of the grease with it to bring the skinsinto a condition for tanning to produce strong leather.

' In testimony whereof I aflix my signature.

OHARLEStLEMENT KROUSE. 

